THE BREEDING OF THE NORTH ATLANTIC FRESHWATER-EELS
151
attention to the urine production, when discussing the change in
weight taking place in eels transferred from fresh to salt water.
Apart from the facts from lake Tunis and the male silver eels in
brackish wattbr, cxperimonts-whioh I l i i d i i r t dligontly pli~nii~~dhavc definitely shown that neither a dchytlration iior a deniineralization
of the female silver eel in fresh water is a fact in the normal play of
Nature (Koch, 1949; B’ontainc and Koch, 1950). In passing I have
been permitted to cite Prof. Koch’s reccnt letter to me : “ Not a single
one of the silver eels that I manipulated in Denmark did show any sign
of weakness. Some of the specimens came from the fresh-water of the
lake Furesi), other ones were caught in thc Baltic. Afterwards I had
many specimens caught in the Meuse and Scheldt in Belgium and they
too were very vigorous. The same remark was made to me for freshwater silver eels by Miss W. Frost (Windermere) and Miss R. M. Lowe
who at Windermere (in the English Lake District) manipulated a very
large number of specimens caught in the Lake District on their downstream migration. Even after having been kept without food for
months in fresh water, silver eels are still very strong, &B I saw myself
in Belgium.”
It is also important to note that the European eel sometimes starts
its migration towards the sea before it is in the typical silver phase
(Frost, 1946, j p 47-48). Frost has mado observations on all eels caught
in a trap fishing the whole width of a strcam which is the outflow of a
lake: “ Some of the eels caught, although clearly seaward migrante,
had not developed fully these characteristics but were turning from the
yellow to the silver phase. When the trap was first used no distinction
between the fully silver and the transitiond form waa made, although
later the two forms were dintinguinhccl, with thc reAult thd, of thc? no
migrants containing food 21 (IS? and 3dl may be takcn a8 silver eel#,
the remainder being in the transitional forms, although probably
including some silver specimens.”
This does provide some evidence that the silvor eel takcs food on
its migration towards the sea, and, thereforc, this is anotttcr proof that
it is not in a state of debility as Tucker (I95Oe, p. 498) anxcrtn.
Tucker (1959a, p. 500) cites Callamand and Fontaine ( l ! ~ )
in nupport
of his view that the debility of the female d v e r eel in due to dnmirlcrslization. This is only possible if Tucker can prove that Koch (194O) is
wrong when he shows that the apparent dehydration is only due to the
deposition in the muscles of an increasing amount, of fat which is a nonsolvent phase for water. If the degree of hydration is calculated
relative to tho amount of protein prestmt in tho musoIes, there is no
differonco bctweeii a yollow and a silver crel,.whoth from freuh water or
151
attention to the urine production, when discussing the change in
weight taking place in eels transferred from fresh to salt water.
Apart from the facts from lake Tunis and the male silver eels in
brackish wattbr, cxperimonts-whioh I l i i d i i r t dligontly pli~nii~~dhavc definitely shown that neither a dchytlration iior a deniineralization
of the female silver eel in fresh water is a fact in the normal play of
Nature (Koch, 1949; B’ontainc and Koch, 1950). In passing I have
been permitted to cite Prof. Koch’s reccnt letter to me : “ Not a single
one of the silver eels that I manipulated in Denmark did show any sign
of weakness. Some of the specimens came from the fresh-water of the
lake Furesi), other ones were caught in thc Baltic. Afterwards I had
many specimens caught in the Meuse and Scheldt in Belgium and they
too were very vigorous. The same remark was made to me for freshwater silver eels by Miss W. Frost (Windermere) and Miss R. M. Lowe
who at Windermere (in the English Lake District) manipulated a very
large number of specimens caught in the Lake District on their downstream migration. Even after having been kept without food for
months in fresh water, silver eels are still very strong, &B I saw myself
in Belgium.”
It is also important to note that the European eel sometimes starts
its migration towards the sea before it is in the typical silver phase
(Frost, 1946, j p 47-48). Frost has mado observations on all eels caught
in a trap fishing the whole width of a strcam which is the outflow of a
lake: “ Some of the eels caught, although clearly seaward migrante,
had not developed fully these characteristics but were turning from the
yellow to the silver phase. When the trap was first used no distinction
between the fully silver and the transitiond form waa made, although
later the two forms were dintinguinhccl, with thc reAult thd, of thc? no
migrants containing food 21 (IS? and 3dl may be takcn a8 silver eel#,
the remainder being in the transitional forms, although probably
including some silver specimens.”
This does provide some evidence that the silvor eel takcs food on
its migration towards the sea, and, thereforc, this is anotttcr proof that
it is not in a state of debility as Tucker (I95Oe, p. 498) anxcrtn.
Tucker (1959a, p. 500) cites Callamand and Fontaine ( l ! ~ )
in nupport
of his view that the debility of the female d v e r eel in due to dnmirlcrslization. This is only possible if Tucker can prove that Koch (194O) is
wrong when he shows that the apparent dehydration is only due to the
deposition in the muscles of an increasing amount, of fat which is a nonsolvent phase for water. If the degree of hydration is calculated
relative to tho amount of protein prestmt in tho musoIes, there is no
differonco bctweeii a yollow and a silver crel,.whoth from freuh water or